1. Field of the Invention
The present invention generally relates to fluid filtration. More particularly, the present invention relates to a cartridge type dual stage filter element bypass valve.
2. Discussion of the Related Art
In order to remove contaminants from a flowing gas or liquid, the contaminated medium is often passed through a filter element in a filter. Filters are commonly used in the lubrication systems of standard internal combustion engines, e.g., automotive engines, truck or heavy equipment engines, and stationary power sources, e.g., computer numerical control (CNC) machines, injection molds, die cast machines, compressors etc.
Engine oil lubrication systems, which are typical of many fluid systems, frequently include a filter assembly which has a filter formed from a porous filter medium for removing damaging particles from the lubricating oil utilized in the system. Mechanical wear within the engine, the outside environment, and contaminants accidentally introduced during normal servicing provide a source of large particles which may plug lubricating nozzles or severely damage parts and create excessive wear on any surfaces relying on a thin film of the lubricating oil for protection.
Filtration systems used in these applications generally include a cylindrical housing into which a cylindrical filter is placed to remove particulate materials from fluids such as oil. Two types of filter assemblies have commonly been used in lubrication system applications, filter assemblies with removable filter elements and disposable filter assemblies. In a commonly used xe2x80x9cspin-onxe2x80x9d disposable filter assembly, the filter element is sealed in a metal can with a metal core located in the center of the element to provide a support structure. In such systems, to replace a clogged or dirty filter element, it is necessary to replace and dispose of the entire filter assembly.
In many filtration applications, the filter element must be changed periodically. For instance, in automotive applications the oil filter is typically changed every few thousand miles or every few months. There are a limited number of reusable oil filter types available or in use, but in most high quality lubrication systems, spin-on disposable filter assemblies are used, and these can create a disposal problem and are treated as hazardous material.
When filters were first introduced for use in lubrication systems, it was common to utilize cartridge type filter elements that fit into a removable housing. When the filter element needed replacement, the housing was removed from the oil filter mount on the engine, the cartridge was removed from the housing, the housing was cleaned, a new cartridge was installed, and the housing with the new cartridge was then replaced on the engine. Cartridge filters of that type usually included a cellulose filter membrane, exterior metal support, and a supporting center tube typically made of metal mesh or expanded metal. The metal supports, i.e., the center tube or outer wrap, were needed to prevent the filter from being crushed by the pressure generated in the lubricant being filtered. Differential pressures in an automotive lubricating system can rise substantially at engine start-up, and particularly during malfunctions, such as a plugged filter malfunction (due, for example, to water or excess engine wear metals in the oil), and can reach 200 pounds per square inch (psi) or more.
Lubrication systems typically rely upon a pump to force the oil through the filter and then circulate the filtered oil to the moving parts of the engine for lubrication. Oil is forced through the filter by limited pressure developed on the upstream side of the filter by the oil pump. The pressure required to force oil to pass through the filter at a given rate will be greater for more viscous or thick oils or for filters formed from finer pored filter media, i.e., porous filter media having smaller average or mean pore diameters.
It has been recognized that it is necessary in many instances to provide for a continuous flow of a fluid that passes through a filtering device, even after the filtering device has become clogged through extensive use thereof. One method for doing so utilizes a bypass valve. The function of a bypass valve is to respond to a pressure differential buildup caused, for example, by a plugged filter, and bypass oil around the filter. In effect, the bypass valve limits pressures in the system, but at the cost of passing unfiltered oil to the equipment.
To prevent unfiltered oil from passing to the equipment, a bypass valve may be used in combination with a second filter element. Examples of such use of multiple fluid filter elements in prior filtering systems arc illustrated in U.S. Pat. No. 4,783,271 to Silverwater; U.S. Pat. No. 3,283,902 to Farris et al; U.S. Pat. No. 4,038,189 to Dison et al; and U.S. Pat. No. 4,885,082 to Cantoni. All of the prior filter devices illustrated in the aforesaid patents include dual filter systems that are designed to permit flow of the fluid medium to be filtered to continue even though the primary filter may have become obstructed in the use thereof. These prior systems, particularly as illustrated in the Silverwater and Farris et al patents, included concentrically located filters that are disposed in a cylindrical housing, and also include a relief or bypass valve construction that is responsive to back pressure caused by obstruction of the primary filter. However, the prior systems are somewhat complex and unreliable in use. Further, these prior known devices include a number of elements that have to be precisely machined and interfitted which renders the filter assemblies uneconomical in use.
For example, the Silverwater patent discloses a filter assembly which removes particles from a fluid and which comprises two filters, a first structure for directing the fluid first through one filter and then through the other, and a second structure for bypassing both filters. The Silverwater filter provides for a filtered flow through the second filter element whenever the primary element is clogged or so obstructed that the flow-through results in a pressure differential across that element above a predetermined minimum. A second by-pass is provided for the secondary filter element, so that when this element becomes clogged, or so obstructed that the flow-through results in a pressure differential across that element above a predetermined minimum, then all flow through the filter by-passes both the primary and secondary filter elements.
To accomplish the above, the Silverwater filter uses two separate bypass valves. A pressure-sensitive annular spring disc valve is positioned in the inlet passage so as, under normal conditions, to close off a line leading to the secondary filter element. Therefore, all flow must pass through an orifice into the primary filter element. At a predetermined pressure differential on the disc face, the minimum value of which is determined by the flow requirements of the system, the disc valve is actuated in a manner to open the passage between the inlet and secondary filter element. The dimensioning of the orifice is matched with the spring bias force of the disc and the dimensioning of the disc force exposed to fluid pressure, so as to obtain actuation of the disc valve at the predetermined fluid pressure differential. The second bypass valve functions in a similar manner with the dimensioning of the orifice being matched to the spring bias force.
It is important to note that the design of each bypass valve is application specific in the Silverwater filter. A new application would require a redesign and remanufacture of the entire filter assembly. The disc valve of the Silverwater filter is in the form of a disc bowed against the direction of flow and which opens fully at a predetermined pressure differential. The flow through required is provided by dimensioning the disc and valve seat so as to give an annular opening necessary to achieve the predetermined flow capacity when the valve opens. Disk thickness, amount of bow, disk diameter and annular opening diameter are determined by the pressure differential to be resisted, i.e., the resistance to be offered by the spring action of the disc, and the flow capacity needed at a given pressure differential.
The Silverwater filter has several other design disadvantages: The pressure-sensitive annular spring disc valve is relatively costly to manufacture, and requires tight control of its dimensional tolerances. A small variation in the height to thickness ratio changes considerably load-deflection characteristics of the pressure-sensitive annular spring disc valve. Leakage is generally a big problem with this type of design valve mechanism. Cracking pressure (i.e., the pressure required to open the valve) is generally not consistent from part to part due to manufacturing variability and spring rate characteristics. The spring disc valve is generally useful where high loads and small deflection are required and allowable leakage can be high. The design is hard to adjust for a particular valve application. The dual valve is not presented in a replaceable cartridge type design.
An array of filter applications require that the filter elements or cartridges not only be replaceable, but also that various dual filter combinations of filter elements, i.e. different micron removal ratings, be adjustable to meet various system requirements. This of course would also entail the use of bypass valves that can also be easily selected and replaced to meet the various combinations and requirements of the dual filter elements. This is required because the bypass valves are designed to be responsive to a predetermined increase of pressure as a result of back pressure created upon obstruction of the fluid path by a blocked or plugged filter whereby the by-pass valve is moved to an open position. The predetermined increase in pressure as a result of back pressure is in part a function of the porosity of the chosen filter element.
An economical, versatile, and reliable filter assembly is required to utilize replaceable and disposable cartridge type filters. Such a filter assembly requires an easily replaceable cartridge type dual stage filter element bypass valve. As will be described hereinafter, the subject invention includes a cartridge type dual bypass valve that not only provides for the efficient filtering of the fluid medium as required, but ensures continuous flow of the fluid through the dual stage bypass valve when the primary filter and secondary filter elements become obstructed.